Epitaxial substrate for field effect transistor

Abstract

The present invention provides an epitaxial substrate for field effect transistor. In the epitaxial substrate for field effect transistor, a nitride-based Group III-V semiconductor epitaxial crystal containing Ga is interposed between the ground layer and the operating layer, and the nitride-based Group III-V semiconductor epitaxial crystal comprises the following (i), (ii) and (iii). (i) a first buffer layer containing Ga or Al and containing a high resistivity crystal layer having added thereto compensation impurity element present in the same period as Ga in the periodic table and having small atomic number; (ii) a second buffer layer containing Ga or Al, laminated on the operating layer side of the first buffer layer; and (iii) a high purity epitaxial crystal layer containing acceptor impurities in a slight amount such that non-addition or depletion state can be maintained, provided between the high resistivity layer and the operating layer.

Description

TECHNICAL FIELD[0001]The present invention relates to an epitaxial substrate for field effect transistor (hereinafter referred to as “FET”) using a nitride-based Group III-V semiconductor.BACKGROUND ART[0002]A field effect transistor using a nitride-based Group III-V semiconductor epitaxial substrate (hereinafter referred to as “GaN-FET”) is a field effect transistor constituted such that a GaN layer drives as a channel layer, and it is an element which rapidly becomes widely noticed of late from that the GaN-FET has high voltage resistance, high heat resistance and small environmental load of constituent materials as compared with the conventional FET having a structure that an epitaxial semiconductor crystal layer such as GaAs, AlGaAs, InGaAs, InGaP and AlInGaP is used as a channel layer.[0003]The GaN-FET has various types in view of the structure of an operating layer. In particular, the GaN-FET of the type that a two-dimensional electron gas (hereinafter referred to as “2DEG”) i...

AI Technical Summary

Benefits of technology

[0018]An object of the present invention is to provide an epitaxial substrate for field effect transistor that can solve the problems in the prior art.

Problems solved by technology

This leads to the problems of deterioration of pinch-off characteristics and increase in drain leakage.

Furthermore, the unnecessary current component has low mobility different from 2DEG.

As a result, in the case of operating the gate electrode with high frequency voltage, adverse influence such as frequency dispersion is involved.

Additionally, the unfavorable unnecessary current also flows into adjacent other elements, causing the interference such as fluctuation of threshold voltage of the adjacent elements.

In general, nitride-based Group III-V monocrystal has extremely high stability chemically and physically, and deep element isolation processing as reaching the substrate is extremely difficult.

However, it is not easy to epitaxially grow high resistivity nitride Group III-V monocrystal.

Various crystal defects are present in crystal.

However, the above-described prior arts have the following problems on production.

It is known that beryllium has extremely strong toxicity, and load to safety and environment is extremely large.

Thus, the application of beryllium to production is not always practical.

Where carbon is doped in crystal in high concentration, lattice distance of crystal is disturbed, resulting in deterioration of crystallizability.

This gas etches an epitaxial layer, resulting in deterioration of crystallizability.

That is, it is difficult in MOVPE method to control C concentration with good accuracy by only controlling flow rate of a C precursor into a reactor, though the other doping materials is not difficult to be controlled by the flow rate.

Even though the production can be performed by avoiding the above problems on production, where compensation impurities are present in a layer, other disadvantages may be posed in FET characteristics.

Therefore, when the compensation impurities are dispersed in the vicinity of a channel layer, this affects the running itself of channel electrons related to FET operation.

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